1. Field of the Invention
The present invention relates generally to a small gas turbine engine, and more specifically to a rotary fuel injector to supply fuel and air to the combustor.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Small gas turbine engines of the kind used in Unmanned Air Vehicles (UAV) such as a small cruise missile or a drone are well known in the art. These turbines produce a thrust from less than 300 lbs to several hundred lbs. Because these turbine engines must fit within a small space, they tend to be very compact. Since the engine must be compact in size, the combustor must be as small as possible. However, the combustor must provide a long enough burn path to remain lit, and to burn the fuel to produce power without wasting unburned fuel. In small combustors, the fuel droplets size must be small in order to burn in the smaller combustor sections in which the fuel particle residence time for burning the particles is short. Larger fuel particles will take longer to burn and in a small combustor will not burn completely. Effective us of the available volume must be made so that the combustor is able to provide the required heat output over a range of engine operating speeds and flight conditions.
Small expendable gas turbine engines also suffer from poor specific fuel consumption (SFC), which limits the engine to unnecessarily short range and loiter times. Small engines suffer from restricted flight/starting envelopes and operating speeds due to combustor flame-out limitations.
Cup shaped fuel slingers are well known in the art. U.S. Pat. No. 3,983,694 issued to Bracken, Jr. on Oct. 5, 1976 and entitled Cup-Shaped Fuel Slinger shows a slinger to radially sling fuel from a cup shape reservoir and into a combustion zone. The cup includes a lip on a radial outer wall of the cup, and the fuel is forced over the lip by centrifugal force due to rotation of the cup. Other rotary fuel injectors include U.S. Pat. No. 4,870,825 issued to Chapman on Oct. 3, 1989 entitled Rotary Fuel Injection System which includes a hydraulic fuel trap within a U-shaped of the rotary cup; and U.S. Pat. No. 4,040,251 issued to Heitmann et al. on Aug. 9, 1977 entitled Gas Turbine Combustion Chamber Arrangement.
Other types of fuel injection include fuel injectors such as U.S. Pat. No. 3,381,471 issued to Szydlowski on May 7, 1968 entitled Combustion Chamber For Gas Turbine Engines where an injection wheel 27 injects fuel into the combustion space 24 for burning; U.S. Pat. No. 4,996,838 issued to Melconian on Mar. 5, 1991 entitled Annular Vortex Slinger Combustor shows a fuel nozzle for radial outward injection of fuel. U.S. Pat. No. 6,925,812 issued to Condevaux et al. on Aug. 9, 2005 entitled Rotary Injector shows a fuel slinger 20 for slinging fuel into a combustion zone, and a rotary injector 10 having a plurality of injection ports each axially offset and each with a shorter radius in the downstream direction of the engine for injecting fuel into the afterburner section.
U.S. Pat. No. 2,705,401 issued to Allen et al. on Apr. 5, 1955 entitled Vaporizing Means For Liquid Fuel Combustion Chambers shows a generally frustoconical disc-like member 18 with a concave face downstream and concentrically stepped in which fuel is supplied through a pipe 19 to an axial well 20 of the member 18, the well having an annular lip 21 over which the liquid fuel is centrifuged onto the stepped face as a thin film and is vaporized by the heat in the flame chamber. Any fuel remaining unvaporized when it reaches the next radially outer step 22 (which may be undercut) builds up and is centrifuged over the latter for vaporization on the succeeding conical annulus.
An object of the present invention is to provide a rotary cup injector with improved fuel break-up ability and to allow for the use of heavier and contaminated fuels in a small gas turbine engine.
Another object of the present invention is to provide a rotary cup injector with fuel atomization for unassisted cold ignition without the need of expensive and heavy start assist systems.
Still another object of the present invention is to provide a rotary cup injector with rapid vaporization combined with good combustor pressure drop to improve vaporization and mixing of liquid fuels.